Semi-natural grasslands are valuable ecosystems that have a high biodiversity. Unfortunately, a lot of this biodiversity is being lost as semi-natural grasslands are declining in both size and number. Restoration to reestablish semi-natural grasslands is often done by removing shrubs and trees and planting seeds. After this reinstalment of management such as mowing, and grazing is done to keep woody plants away. Grassland management and restoration have a proven positive effect on species richness and abundance regarding vascular plants. Yet little is known about the effects on insects and spiders. By reviewing scientific publications, I explored how insects and spiders are affected by management, as well as how local and landscape factors affect restoration. Grassland history and timing of restoration, as well as insect and spider’s dispersal ability, affects the possibility of a successful restoration. Larger habitats with good connectivity and surrounding supporting habitats are positive factors for viable insect and spider communities. By comparing different publications, some species benefit from intensive grazing and mowing, and some show a negative response. Long-term low to medium intensive management will favor a higher biodiversity compared to short-term intensive management. In conclusion, balancing conflicts and trade-offs is the real challenge when it comes to semi-natural grassland restoration. In general, to benefit as many insect and spider species as possible management should focus on variation in grass height and flower abundance. However, more research on how insect and spiders are affected by grassland restoration is something I believe would benefit future conservation projects.

Natural dispersal mechanisms and biogeographical barriers have shaped species' native distributional ranges over millions of years. However, over the last few centuries, humans have dispersed species beyond their natural ranges. Those species that undergo explosive population growth and rapid expansion in the introduced region are considered as invasive because they have the potential to cause negative effects on desirable species and/or ecosystem services. In chapter II, I identified what ecosystem characteristics are more closely associated with successful establishment of exotic and native species, to have a better idea of where to concentrate our efforts and resources to prevent invasion events while preserving native species. I found that native and exotic species were differently affected by ecosystem properties. Exotic species were favored by human activities and low native species abundance and diversity. However, in Chapter III, I found that species functional traits, such as growth form and phenology, are more important to explain their response to ecosystem characteristics than native status under certain circumstances. The abundance and reproductive capacity of the evaluated plants were reduced when disturbances occurred during their respective active growing periods. This finding suggests that we need to have into account species-specific responses to ecosystem characteristics when managing biological invasions. Chapter IV examined phenotypic differentiation of native, expansive, and introduced populations of Baccharis halimifolia L. occurring in different regions of the world. The results suggest that there are significant phenotypic differences in germination and early growth among native, expansive, and introduced populations, which could have contributed to the success of B. halimifolia in the introduced and expansive ranges. Finally, in Chapter V, I used the information that I learned in the past projects to predict the spread of 45 exotic plants across southeastern United States and evaluated what landscape factors make an area more susceptible to be invaded. I found that the influence of landscape composition and configuration on invasion risk is species-specific. This result suggests that not only we have to consider species functional traits when managing biological invasions, as we saw earlier in the experiment with disturbance timing, but also species habitat preferences.